LD4B how good and how rare what are they worth?

There's an old thread titled Getting the Intake on Intake Manifolds.
This thread contains a pretty thorough list of manifolds, with carb heights and also port sizes.
Without looking at that list, I think the LD4B has the smaller 273/318 ports. If you want the big ports, you want an LD340 manifold.
Hope this helps.
Murph